Definition · Plain-language
Calibration
Calibration is the comparison of a measuring instrument against a reference standard of known accuracy to determine, and where needed correct, its deviation.
The step most authors miss
Doing CRediT right? Don’t stop at the statement.
A CRediT statement credits you inside one paper. The recognition CRediT was built for happens when those roles are tied to you, persistently. Sign in with your ORCID — free — and claim your CRediT contributions on casrai.org, the home of the standard. They become a verified, portable part of your identity, not a line that disappears into one PDF.
Free: claim your contributions, then export a journal-ready CRediT statement, schema.org structured data, JATS XML, CSV or BibTeX — and preview your public profile. A membership publishes that profile publicly and verifies the journals you serve.
What calibration involves
In a calibration, a measuring instrument or measurement standard under test is compared with a reference of higher accuracy under controlled conditions. The result is a statement of how the instrument’s readings relate to reference values, together with the associated measurement uncertainty. This is recorded in a calibration certificate. Calibration tells the user how much the instrument deviates and how confident they can be in its readings; it does not by itself change the instrument. Where the deviation is unacceptable, a separate adjustment may be carried out and the instrument then recalibrated to confirm the effect.
Why calibration matters
Every measuring instrument drifts over time through wear, environmental effects and use, so without periodic calibration its readings cannot be relied upon. Calibration underpins the validity of test and measurement results in laboratories, manufacturing, healthcare and trade. It is a core requirement of laboratory standards such as ISO/IEC 17025, which expects equipment that affects results to be calibrated with traceability to recognised references. Calibration also supports safety and fairness: it ensures that a medical analyser, a weighing scale used in trade, or a pressure gauge reads correctly within known limits.
Calibration and traceability
A calibration is meaningful only if the reference it uses is itself traceable to a higher reference, and so on up an unbroken chain to a primary realisation of an SI unit, usually maintained by a national metrology institute. This is metrological traceability. Each link in the chain is a documented calibration with stated uncertainty, and uncertainty accumulates down the chain. Accredited calibration laboratories, recognised under ISO/IEC 17025, provide calibrations whose traceability and uncertainty are independently assured, which is why their certificates are trusted internationally.
Key facts
At a glance
- Definition: comparing an instrument with a reference standard of known accuracy
- Output: a calibration certificate stating deviation and measurement uncertainty
- Purpose: determine deviation and establish metrological traceability
- Not the same as: adjustment (which may follow a calibration)
- Required by: laboratory standards such as ISO/IEC 17025
- Top of chain: primary SI realisations held by national metrology institutes
Common misconceptions
What people often get wrong
Often heard: Calibration means adjusting an instrument so it reads correctly.
Actually: Calibration is the comparison that determines an instrument’s deviation and uncertainty; it does not change the instrument. Adjustment is a separate step that may follow if the deviation is unacceptable, after which the instrument is recalibrated to confirm the result.
Often heard: Once calibrated, an instrument stays accurate indefinitely.
Actually: Instruments drift through use, wear and environmental effects, so calibration is valid only for a period. Recalibration at appropriate intervals is needed to keep readings within known limits, which is why calibration schedules exist.
Often heard: Any in-house comparison counts as a traceable calibration.
Actually: A calibration only provides metrological traceability if it uses references that are themselves traceable through an unbroken, documented chain to recognised standards. Accredited calibration laboratories provide independently assured traceability and uncertainty.
Going deeper
